1. Field of the Invention
The present invention is directed to a tape cartridge which contains magnetic recording tape, in particular a cartridge containing an extremely wide tape which allows fast access time to data recorded on the tape, as well as a drive unit for such a tape cartridge.
2. Description of the Prior Art and Related Subject Matter
The use of magnetic tape as a medium for data recording has the significant advantages of a relatively low cost and a relatively large recording surface area. Nevertheless, conventional magnetic tape has certain disadvantages associated therewith.
A first of these disadvantages is that tape is a sequential medium, which means that when a data transfer head is located at a beginning of a tape, it is necessary for the tape to be transported along its entire length in order to retrieve (or re-write) information at the end of the tape.
A second disadvantage is that, due to the desire and necessity of storing as much data as possible within an available tape area, the data transfer head technology as well as the recording media technology are pushed to their quality limits.
Moreover, many existing drives and cartridges must be designed within specified form factors, in order to satisfy standardization requirements. As an increasing number of functions become available, which are desired to be accommodated in a drive or on a tape, data storage area or other functions must be sacrificed to accommodate the new, additional functions, or some type of compromise must be reached in the overall design.
Among the more important market requirements which are expected in the near future for data storage on tape is that the need for higher storage capacity will continue to increase, at an even faster rate than previously. As discussed below, for example, the storage capacity of a currently available single cartridge is not sufficient for unattended backup during a longer period of time, and therefore so-called autoloader systems have been developed to automatically insert and remove a number of cartridges in a sequence.
Further market requirements are expected to be a need for faster time to access data, a need for an increased data transfer rate, a lower cost per MB (megabyte) and an overall improved quality and reduced cost.
As noted above, the limited data storage capacity of conventional cartridges has resulted in the development of autoloader systems. Conventional autoloader systems, however, are not a satisfactory solution to the problem of storing a large amount of data in an unattended backup procedure over a relatively long period of time. Several disadvantages exist with regard to currently available autoloader systems.
Because such autoloader systems make use of a large number of cartridges, the cartridges are made relatively small, and therefore have a limited space available for use for data storage. Typically, six to ten of such cartridges must be put in a magazine in order to have sufficient storage area (capacity). Because of the relatively small size of the cartridges, the drive is also made small, in order to match standardized form factors. The drive is disposed in a system housing, which also contains robotics, electronics and software needed for loading an unloading the cartridges.
The relatively large number of components, and therefore the relatively high cost, associated with conventional autoloader systems makes the use of such systems an unattractive alternative for a customer who merely wants long term data backup.
To address these problems, a tape cartridge and a drive for extremely wide tape are disclosed in co-pending U.S. application Ser. No. 09/691,165, filed Oct. 19, 2000, the teachings of which are incorporated herein by reference. The tape cartridge and drive described therein accommodate tape having an extremely wide width, such as a width that is greater than approximately 24 mm, or in a range between approximately 24 mm and approximately 127 mm.
The width of this extremely wide tape, therefore, is greater than that of a conventional magnetic recording tape by a factor of 6 to 10 times. Because the tape has this extremely wide width, the total tape length can be made significantly shorter while still making the same total area available for data storage. Making the tape shorter, however, requires less time for winding and unwinding the tape from the hubs on which it is carried in order to access data at a particular location on the tape.
It is important, however, that the housing for accommodating such extremely wide tape have the same, or substantially the same, form factor as conventional recording cartridges, so as to be accommodated in the openings for conventional tape cartridges in tape drives and auto loaders and magazines. This means that the axes of rotation of the tape hubs in cartridges for accommodating extremely wide tape will proceed parallel to a “longer” dimension of the cartridge housing, rather than perpendicular to the shortest dimension (height) as in a conventional cartridge housing. Given a length of extremely wide tape which is necessary to provide the same total area available for recording data on the tape as a conventionally sized tape, such a length of extremely wide tape can be accommodated in a housing having a height which is comparable to the height of a conventional tape cartridge only when the tape is substantially evenly distributed in respective tape packs on the two hubs in the housing. When any significant amount of extremely wide tape is wound onto one of the hubs, the diameter on the tape pack on that hub increases beyond the standard height of a conventional cartridge housing.
This problem could be addressed by simply providing a lesser length of extremely wide tape in the cartridge, so that even when all of the tape is wound on one tape hub in one tape pack, the diameter of that tape pack still would not exceed the height of a standard tape cartridge.
This would defeat one of the advantages of employing extremely wide tape, however, by decreasing the total area available for recording data.
To allow a longer length of wide magnetic recording tape to be accommodated in a tape cartridge having a size which conforms to a standard form factor, co-pending U.S. application Ser. No. 09/859,328, filed May 16, 2001, the teachings of which are incorporated herein by reference, discloses a tape cartridge for wide magnetic tape, and a drive therefor, wherein the cartridge housing is formed by two parts which are slidable relative to each other along the direction of the housing height. When the two cartridge portions are in a non-expanded state, the cartridge exhibits a standard form factor, so that it can be inserted into conventionally sized openings in storage and drive equipment. After insertion in a tape drive of the type also disclosed in this co-pending application, the housing portions are slidably moved apart so as to have an interior spacing therebetween which allows substantially all of the tape to be wound in a single tape pack on one of the hubs. For storage purposes, the tape is wound in two tape packs of substantially equal diameter on the respective hubs, thereby allowing the aforementioned standard form factor to be maintained, but in use, as noted above, it is possible for all of the tape to wound on only one of the hubs, without being limited by the interior dimension of the cartridge.
In some circumstances, however, the access time to data stored on the magnetic tape still may be not be sufficiently rapid.